All VPON products are Linux based embedded system with OS and DVR software in one single DOM chip. As the DOM chip is actually an IC component, customers do NOT have to install any software into the DVR unit. It operates automatically when power on. Recorded video data is stored in separate independent hard drives and any hard disk problem does NOT effect kernel operations of the DVR. This arrangement makes DVR maintenance much easier than those that install OS and DVR software on the same hard disk for video storage because customers need NOT re-install everything when the system hard disk fails. The Linux based OS also has better virus protection capability because all of the un-necessary TCP/IP ports are closed to give NO chance for virus intrusion. For more detail information, please visit VPON web page at http://www.vpon21.com.